a. Field of the Invention
This invention relates to methods for converting organic materials into ethanol.
b. Background of the Invention
Ethanol is a chemical compound having the formula C20H6. Ethanol includes two carbons connected to a hydroxyl unit. Ethanol is flammable with a flash point of approximately 13° C. and a boiling point of approximately 78° C. It is completely miscible with water. It is a volatile, colorless liquid with a strong order, and it tends to burn with a smokeless blue flame which is not always visible in normal light. Ethanol has a characteristic azeotrope with water. When mixtures of ethanol and water are distilled at atmospheric pressure, the maximum concentration of ethanol in the overhead distillate is approximately 96% by volume, with the remaining 4% by volume of the overhead distillate being water. Ethanol has a specific gravity of approximately 0.789 grams per cubic centimeter, and a chemical abstract services, or CAS number of 64-17-5.
When pure ethanol is mixed with pure water, the resulting solution has less volume than the two components. So if one liter of pure ethanol was mixed with one liter of pure water, the resulting mixture would have a volume of less than two liters. The mixture is also exothermic and will give off heat, so when pure ethanol is mixed with water the resulting solution will be warmer than the combination of just the ethanol and the water. Ethanol is the alcohol that is commonly consumed in beverages such as beer, wine and liquor and is responsible for the intoxicating effects of alcohol on people.
There are many uses for ethanol. For example, ethanol has many advantageous properties when used as a solvent. It has a polar end and a non-polar end such that many compounds will be soluble in ethanol, where the more polar compounds are attracted to the hydroxyl (OH) group attached to the ethanol, and the non-polar compounds are attracted to the ethyl group on the opposite end of the molecule. Ethanol can be used as a raw material in the production of many compounds. These compounds include ethyl halides, diethyl ether, ethyl esters, butadiene, acetic acid, and ethylamines, amongst others. Ethanol is also used as an antiseptic, and can be included in medical wipes and in certain antibacterial hand sanitizer gels. Ethanol tends to kill organisms by denaturing their proteins and dissolving their liquids, and it is effective against many bacteria, fungi and also many viruses. It can be used as a food source, although it is intoxicating
Ethanol can also be used as fuel. It has been used as rocket fuel in certain early bio-propellant rocket vehicles, where it was used in conjunction with an oxidizer. It can be used with ethanol fuel cells to produce electricity. It can also be used as a fuel for combustion in automobiles. Varying concentrations of ethanol are used as fuel for automobiles and other vehicles. Many fuels available in the United States include ethanol at concentrations up to 10%. There are also E85 cars which can bum ethanol at concentrations of 85%, with the remaining 15% being a petroleum based fuel. The E85 fuels tend to store less energy per liter than petroleum based fuels, such as gasoline. Therefore, the efficiency in miles per gallon of a vehicle using 85% ethanol will typically be less than for a comparable vehicle using pure gasoline.
Ethanol is frequently produced industrially by fermentation processes. For example, a source of organic material, such as a food source, can be inoculated with yeast. The yeast will then begin to consume the organic material, and give off ethanol as a metabolic waste product. There are other micro-organisms that can be used in place of yeast for fermentation. These other micro-organisms include Zymomonas Mobilis and Escherichia Coli, as well as others. Ethanol produced by micro-organisms tends to be toxic to the micro-organisms, so when ethanol is produced above certain levels it inhibits the micro-organisms and stops the fermentation process. Micro-organisms are more efficient at converting some sorts of organic compounds than others. The commonly used baker's yeast tends to be more efficient at converting sugars in such things as sugar cane or corn than in converting cellulosic materials into ethanol. Most ethanol production in the world now is based on organic materials with high sugar content, such as corn or sugar cane.
There have been many attempts to come up with efficient methods for efficiently converting cellulosic materials to ethanol, and these have met with varied success. Many times the use of cellulosic feed sources will involve some sort of pre-treatment technique to make the cellulose available to the micro-organisms. This can include acid hydrolysis, steam explosion, ammonia expansion, alkaline wet oxidation or ozone pre-treatment, amongst others. It is also possible to produce ethanol by means other than fermentation, such as gasification.
After the fermentation process, the ethanol is typically recovered from the fermentation mash. This is frequently done through distillation, and the ethanol is recovered with water as an azeotrope. There are other techniques of recovering ethanol from a fermentation mash which could be used. There are also ways to recover pure ethanol from an azeotropic mixture of water and ethanol. For example, the collected overhead ethanol and water can be run through a carbon absorption system to absorb the water, leaving essentially pure ethanol.
In the fermentation process, carbon dioxide is generated as a by-product, and this carbon dioxide typically bubbles out of the fermentation mash. The fermentation of an organic material with microorganisms is typically done anaerobically, or not in the presence of oxygen. When little or no oxygen is present, the micro-organisms find energy from the food source and not from available free oxygen. Many micro-organisms, including some yeasts, will utilize different mechanisms for consuming organic materials in anaerobic vs. aerobic conditions. Some yeast will preferentially produce water instead of ethanol as a by-product of metabolism when oxygen is present.